Debugging/Stepping into a package module via cabal repl

Question

So I have the following code from Preventing caching of computation in Criterion benchmark and my aim is to be able to step from main directly into the function defaultMain in Criterion.Main :

{-# OPTIONS -fno-full-laziness #-}
{-# OPTIONS_GHC -fno-cse #-}
{-# LANGUAGE BangPatterns #-}
module Main where
import Criterion.Main
import Data.List

num :: Int
num = 100000000

lst :: a -> [Int]
lst _ = [1,2..num]

myadd :: Int -> Int -> Int
myadd !x !y = let !result = x + y in
  result

mysum = foldl' myadd 0

main :: IO ()
main = defaultMain [
  bgroup "summation" 
    [bench "mysum" $ whnf (mysum . lst) ()]
  ]

and the cabal file is :

name:                test
version:             0.1.0.0
build-type:          Simple
cabal-version:       >=1.10

executable test
  main-is:             Main.hs
  build-depends:       base >=4.8 && <4.9,
                       criterion==1.1.0.0
  default-language:    Haskell2010
  ghc-options:         "-O3"

(using ghc 7.10.1 and cabal 1.22.0.0).

If from within cabal repl I try to set a breakpoint in criterion I get the following error :

*Main> :break Criterion.Main.defaultMain
cannot set breakpoint on defaultMain: module Criterion.Main is not interpreted

Furthermore if I try to add the package I get the following error :

*Main> :add *Criterion

<no location info>: module ‘Criterion’ is a package module
Failed, modules loaded: Main.

If I do within the directory git clone https://github.com/bos/criterion and then add the following two lines to my cabal file :

other-modules:       Criterion
hs-source-dirs:      .
                 ./criterion

then upon doing cabal build I get the following errors :

criterion/Criterion/IO.hs:23:0:
     error: missing binary operator before token "("
     #if MIN_VERSION_binary(0, 6, 3)

so I suspect that I have to do a full on merge of the criterion cabal file with my cabal file above, which feels a bit excessive.

Is there an easier way for me to go about setting a breakpoint in Criterion, so that I can step (when debugging in cabal repl/ghci) directly from my source into criterion's source? Thanks

p.s. There is a related question at Debugging IO in a package module inside GHCi but unfortunately it did not help.

Answer 1

This is how I managed to achieve the desired goal of being able to step (within cabal repl) from my code into the criterion source :

1. First do :

   mkdir /tmp/testCrit
   cd /tmp/testCrit
   

2. Download criterion-1.1.0.0.tar.gz

3. Unzip into /tmp/testCrit, so we should have /tmp/testCrit/criterion-1.1.0.0. In this directory we have Criterion.hs etc.

4. Then jump into the folder containing the criterion source and do :

   cd /tmp/testCrit/criterion-1.1.0.0
   cabal sandbox init
   cabal install -j
   

   Note that this creates a directory : /tmp/testCrit/criterion-1.1.0.0/dist/dist-sandbox-782e42f0/build/autogen which we shall use later

5. Back in /tmp/testCrit create a Main.hs file containing the benchmark code above and also the cabal file above, but merge it with the criterion cabal file contained in /tmp/testCrit/criterion-1.1.0.0 in the following way. Note the main new additions are the lines :

   cc-options: -fPIC
   

   which allows one to run it in cabal repl, and the following lines :

   hs-source-dirs: 
     ./
     ./criterion-1.1.0.0
     ./criterion-1.1.0.0/dist/dist-sandbox-782e42f0/build/autogen
   

   The full cabal file should then look like :

     name:                test
     version:             0.1.0.0
     build-type:          Simple
     cabal-version:       >=1.10
   
     executable test
       main-is:             Main.hs
       build-depends:       
         base >=4.8 && <4.9,
         aeson >= 0.8,
         ansi-wl-pprint >= 0.6.7.2,
         base >= 4.5 && < 5,
         binary >= 0.5.1.0,
         bytestring >= 0.9 && < 1.0,
         cassava >= 0.3.0.0,
         containers,
         deepseq >= 1.1.0.0,
         directory,
         filepath,
         Glob >= 0.7.2,
         hastache >= 0.6.0,
         mtl >= 2,
         mwc-random >= 0.8.0.3,
         optparse-applicative >= 0.11,
         parsec >= 3.1.0,
         statistics >= 0.13.2.1,
         text >= 0.11,
         time,
         transformers,
         transformers-compat >= 0.4,
         vector >= 0.7.1,
         vector-algorithms >= 0.4
       default-language:    Haskell2010
       ghc-options:         "-O3"
       c-sources: 
         ./criterion-1.1.0.0/cbits/cycles.c
         ./criterion-1.1.0.0/cbits/time-posix.c
       hs-source-dirs: 
         ./
         ./criterion-1.1.0.0
         ./criterion-1.1.0.0/dist/dist-sandbox-782e42f0/build/autogen
       cc-options: -fPIC
   

6. Then in the main directory do :

   cd /tmp/testCrit/
   cabal sandbox init
   cabal install -j
   

7. Then we can spin up a cabal repl and step directly into criterion from our Main.hs code :

   *Main> :break Criterion.Main.defaultMain
   Breakpoint 0 activated at criterion-1.1.0.0/Criterion/Main.hs:79:15-43
   *Main> main
   Stopped at criterion-1.1.0.0/Criterion/Main.hs:79:15-43
   _result :: [Benchmark] -> IO () = _
   [criterion-1.1.0.0/Criterion/Main.hs:79:15-43] *Main> :step
   Stopped at criterion-1.1.0.0/Criterion/Main.hs:(131,1)-(147,39)
   _result :: IO () = _
   [criterion-1.1.0.0/Criterion/Main.hs:(131,1)-(147,39)] *Main> :step
   Stopped at criterion-1.1.0.0/Criterion/Main.hs:(131,29)-(147,39)
   _result :: IO () = _
   bs :: [Benchmark] = [_]
   defCfg :: Criterion.Types.Config = _
   [criterion-1.1.0.0/Criterion/Main.hs:(131,29)-(147,39)] *Main> :step
   Stopped at criterion-1.1.0.0/Criterion/Main.hs:132:10-37
   _result :: IO Criterion.Main.Options.Mode = _
   defCfg :: Criterion.Types.Config = _